Thermoelectric pulse generator for motor vehicles

ABSTRACT

A pulse generator arrangement in which a heat-sensitive bimetallic snap disc is connected to a heating circuit when in its initial position. After being heated by current passing directly through the snap disc, the element moves to an actuated position in which a second circuit becomes closed. In the second circuit, the bimetallic snap disc becomes subjected to a lower heating current and thereby cools to a temperature required for the disc to snap back to its initial position. A motor and control circuit operating in conjunction with the snap disc serves for intermittent operation of windshield wipers in a motor vehicle.

United States Patent Ursel 1 Dec. 26, 1972 [54]. THERMOELECTRIC PULSE [56] References Cited ENERATOR FOR MOTOR VEHICLES G UNITED STATES'PATENTS [72] Inventor: Eckhard Ursel, Kappelrodeck, Germany 2,838,645 6/1958 Welch ..337/41 X 2,428,525 10/1947 Osterheld ....337/87 X A :RbetB hG..b.H Sttt t, [73] Sslgnee g r osc m u gar Primary Examiner-Herman J. l-lohauser Attorney-Michael S. Striker [22] Filed: Marchl, 1972 21 Appl. No; 230,759 v ABSTRACT A pulse generator arrangement in which a heat-sensitive bimetallic snap disc is connected to a heating cir- [30] Fomg" Apphcmon Prim! Data cuit when in its initial position. After being heated by March 10, 1971 Germany ..P 21 11 447.6 current Passing directly through the p disc, the

' ment moves to an actuated position in which a second circuit becomes closed. In the second circuit, the [52] US. Cl. ..307/l06, 337/41, 337/86, bimetallic Snap disc becomes subjected to a lower v 337/107 337/337 337/363. 307/117 heating current and thereby cools to a temperature [51] Int. Cl. ..H0lh 35/00 Iequired for the disc snap back to its initial posi [58] new Search-337,41 tion. A motor and control circuit operating in conjunction with the snap disc serves for intermittent operation of windshield wipers in a motor vehicle.

10 Claims, 2 Drawing Figures THERMOELECTRIC PULSE GENERATOR FOR MOTOR VEHICLES BACKGROUND OF THE INVENTION The present invention relates to a thermoelectric pulse generator used in particular for intermittent operation of windshield wipers in motor vehicles. An adjustable resistor determines the heating effect of a thermal-sensitive adjusting element, and thereby the pulse frequency of the pulse generator.

In conventional pulse generators of the preceding species, the pulse duration is regulated by varying the magnitude of the heating current of the thermal-dependent adjusting element, when in the initial position. This arrangement has the disadvantage that the pulse frequency can be regulated or varied only in relatively narrow limits. At the same time, an essential part of the pulse'duration, the cooling interval of the positioning element, becomes only little influenced by the current which gives rise to the heating effect, and thereby the cooling interval remains substantially constant. In addition, the temperature of the environment in the conventional pulse generators can have a significant effect upon the pulse frequency, and this is undesirable in many situations.

SUMMARY OFTHE INVENTION Accordingly, it is an object of the present invention to provide a thermoelectric'pulse generator in which the pulse frequency may be regulated within wide limits, and which is independent of the surrounding temperature. I

Anotherobject of the present invention is to provide an arrangement of the foregoing character which may be readily fabricated and easily assembled.

A still further object of the present invention is to provide an arrangement, as described, which may be economically constructed and maintained.

The objects. of the present invention are achieved by providing that the heat-sensitive positioning element closes a first circuit when in its initial position. In this latter position, heating current flows through the element until it becomes actuated. Upon such actuation of the element a second circuit is closed through an adjustable resistor, whereby current also flows to result in a heating effect on the positioning element. The magnitude of this latter current is less than the heating current before-hand. As a result of this lesser current, the positioning element cools off upon the required temperature difference, to permit the element to return to its initial position.

A simpler arrangement is obtained when the heating current for the positioning element is passed directly through the element itself.

The positioning element can be advantageously in the form of a bimetallic snap disc which closes a first pair of contacts for one current circuit, and a second pair of contacts for the other circuit.

It is particularly advantageous, when in accordance with the present invention the pulse generator is used for intermittent operation of windshield wipers in motor vehicles. In this case, the required current pulse flows through the thermal positioning element, when in the initial position for the purpose of operating the wiper motor. The motor, thereby, has current applied to it, through conventional limit switch, until the wipers have executed a full to-from cycle. The wiping intervals lying between .the individual pulses can be set to any desired value in view of the current which may be finely regulated in passage through the positioning element during the cooling phase. Such regulation of the current may be made over wide limits.

The novel features which are considered as characteristic for the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description'of specific embodiments when read in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an electrical circuit diagram of the pulse generator arrangement, in accordance with the present invention;'

FIG. 2 is a graphicalrepresentation of the function of parameters associated with the arrangement of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawing, the cleaning arrengement in accordance with the present invention, has a DC motor 10 with permanent magnet excitation. This motor 10 is switched on and off, in the conventional manner through a manually operated switch 11. In the position b of the switch 11, the motor 10 drives two windshield wipers, not shown, in a to-from manner. In preparing to switch off the arrangement by setting the manually operated switch 11 to the off position a, the motor 10 receives current until the wipers have arrived to their initial or parking positions, by way of the circuit path from the positive terminal of a current source, the line 12, a limit switch 13, and the line 14. When in the position a of the switch 11, the limit switch 13 becomes actuated by the motor 10 so that this limit switch assumes the position shown in the drawing. In this shown position of the limit switch 13, the current path to the motor is interrupted, and ground potential is applied to the switched motor terminal, through the line 15, line 14, switch 11. By applying ground potential to both terminals of the motor in this manner, braking action of the motor is obtained.

Connected in series with the line 14, is a switching contact 16 which is actuated by a relay coil 17. This switching contact 16 is in the line 14 which leads from the limit switch 13 to the manually operated switch 11. In the initial position, this switching contact 16 interrupts the circuit path between the limit switch 13 and the manually operated switch 11, whereby the line 14 becomes directly connected to the line 12 leading to the voltage source. The relay coil 17 lies within a current path leading from the positive terminal of the current source, to a second manually operated switch 18. The latter serves for intermittent operation of the wipers. From there the circuit leads to a first contact pair 19,19 of a thermoelectric pulse generator 20. The other terminal of the relay coil 17 is connected to ground potential.

The pulse generator 20 has a thermal-dependent positioning element in the form of a bimetallic snap disc 21 which serves directly as a contact element. This contact element becomes heated as a result of current flowing through it. The bimetallic disc 21 is held at its center, and when not heated, the disc 21 lies on the first contact pair 19,19. The pulse generator has a second pair of contacts 22,22 against which the bimetallic disc 21 becomes located upon being heated and actuated thereby. The pair of. contacts 22,22 lie within a line 23 which includes a series-connected adjustable resistor 24. One terminal of this resistor 24 is connected to ground potential. The movable contact of the adjustable resistor 24 is coupled to the switching shaft of the manually operated switch 18. As a result of this coupling, this switch-18 is turned on and off, as well as the value of the resistor 25 becomes set, simultaneously.

Connected in parallel with the relay coil 17, is a resistor 25,which serves, furthermore to determine the heating current through the bimetallic disc 21, when in the position shown in the drawing.

The functional operation of the pulse generator, may be described in what follows, in relation to the diagram of FIG. 2.

To switch on thewipers for continuous operation, the manually operated switch 11 is brought into the position b, whereby the motor 10 has current applied to it. The switch 18 remains open so that all circuit elements connected in series with this switch remain without current, and the switching contact 16 is, thereby, in the position shown in the drawing. Upon turning off the switch 11, the motor 10 still receives current until the wipers have attained their initial or parking positions, through the circuit path including the line 12, limit switch 13, contact 16, line 14, and the manually operated switch 11.

For intermittent operation of the wipers, the manually operated switch 18 is to be closed, so as to close the circuit from the positive terminal of the current source to the relay 17, through the bimetallic disc 21 of the pulse generator 20. In this manner the switching contact 16 is transferred to the actuated position. In this latter position, the contact 16 interrupts the braking circuit through the limit switch 13, and establishes a circuit from the positive terminal of the current source to the motor. As a result, the motor operates or turns and the limit switch 13 becomes thereby also actuated.

In view of the relatively low resistance value of the resistor 25, a relatively large current flows to the bimetallic disc 21, so that the pulse generator becomes actuated within approximately half a second. The pulse generator thereby disconnects the current path to the relay 17, so that the switching contact 16 is returned to the position shown in the drawing, and the limit switch 13 is returned to its operative state. The motor 10 now line 23 and the bimetallic disc 21. The magnitude of the current is determined through the setting of the resistor 24, and is thereby pre-selectable. The adjustable range of the resistor 24 is to be established so that even upon the smallest resistance setting of this resistor, the current flowing through the line 23 is to be still smaller than the heatingcurrent flowing through the pair of contacts 19,19. This condition is imposed so that the bimetallic disc 21 experiences cooling in every case inspite of the heating effect. The cooling leads to the condition after a predetermined time interval, where the bimetallic disc 21 snaps back to its initial position, and the motor pass current again applied to it for a brief period of time through the relay 17.

The time interval which the bimetallic disc 21 requires from its actuated state upon full heating, until it snaps back to its initial position, canbe established or determined within predeterminedlimits, through the resistor 24. FIG. 2 indicates the dependency of the time t on the current I which flows through the second pair of contacts 22,22. The time parameter is determined by the setting of resistor 24, and the diagram of FIG. 2 corresponds to a predetermined pulse generator type. From this diagram of FIG. 2, it is evident that the time interval t can be adjusted between 1.5 and 8 seconds which is sufficient for many applications.

It ,will be understood that each of the elements described above, or two or more together, may also find a useful application in other types of thermoelectric pulse generators for motor vehicles differing from the types described above.

While the invention has been illustrated and described as embodied in a thermoelectric pulse generator for motor vehicles, it is not intended to be limited to the details shown, since various modifications and structural changes may be made without departing in any way from the spirit of the present invention.

Without further analysis, the foregoing will so fully reveal the gist of the present invention that others can, by applying current knowledge readily adapt it for various applications without omitting features that, from the standpoint of prior art, fairly constitute essential characteristics of the generic or specific aspects of this invention and, therefore, such adaptations should and areintended to be comprehended within the meaning and range of equivalence of the following claims.

What is claimed as new and desired to be protected by Letters Patent is set forth in the appended claims.

I claim:

1. A pulse generator, comprising, in combination, a heat-sensitive movable element having a first position when in a substantially low-heated state and having a second position when in a relatively high-heated state; first circuit means connected to said heat-sensitive movable element and closed when said element is in said first position, the current in said first circuit means passing through said element when in said first position and heating said element; second circuit means closed when said element is in said second position, said element moving from said first position to said second position after predetermined heating by said first circuit means, said second circuit means heating said element in said second position with current having a smaller magnitude than the current of said first circuit means, said element cooling under the passage of said smaller current to a predetermined temperature for returning said element to said first position; and means for regulating the magnitude of the current in said second circuit means for regulating the pulse frequency of said pulse generator.

2. The pulse generator as defined in claim 1 wherein said regulating meanscomprises an adjustable resistor.

3. The pulse generator as defined in claim 1, wherein said first circuit means comprises electrical contact means closed when said element is in said first position, said contact means being opened when said element moves from said first position to said second position.

4. The pulse generator as defined in claim 1 wherein the current in said first circuit means passes directly through said element when in said first position for heating said element.

I 5. The pulse generator as defined in claim 4, wherein said first circuit means comprises contact means, the

circuit means including first contact means closed by said bimetallic snap disc when in said first position, said second circuit means including second contact means closed when said bimetallic snap disc is in said second position.

7. A pulse generator as defined in claim 5, including circuit load means connected in series with said element when in said first position. I

8. The pulse generator as defined in claim 7, including resistor means connected in parallel with said circuit load means.

9. The pulse generator as defined in claim 8, including manually operated switching means connected to said first circuit means and said second circuit means for switching the pulse output signal of said pulse generator, said regulating means comprising variable resistor means connected in circuit with said switching means.

' 10. The pulse generator as defined in claim 1, including motor means; and control circuit means connected to said first circuit means and said second circuit means for controlling the operation of said motor in relation to the position of said element. 

1. A pulse generator, comprising, in combination, a heatsensitive movable element having a first position when in a substantially low-heated state and having a second position when in a relatively high-heated state; first circuit means connected to said heat-sensitive movable element and closed when said element is in said first position, the current in said first circuit means passing through said element when in said first position and heating said element; second circuit means closed when said element is in said second position, said element moving from said first position to said second position after predetermined heating by said first circuit means, said second circuit means heating said element in said second position with current having a smaller magnitude than the current of said first circuit means, said element cooling under the passage of said smaller current to a predetermined temperature for returning said element to said first position; and means for regulating the magnitude of the current in said second circuit means for regulating the pulse frequency of said pulse generator.
 2. The pulse generator as defined in claim 1 wherein said regulating means comprises an adjustable resistor.
 3. The pulse generator as defined in claim 1, wherein said first circuit means comprises electrical contact means closed when said element is in said first position, said contact means being opened when said element moves from said first position to said second position.
 4. The pulse generator as defined in claim 1 wherein the current in said first circuit means passes directly through said element when in said first position for heating said element.
 5. The pulse generator as defined in claim 4, wherein said first circuit means comprises contact means, the current in said first circuit means and passing through said element for heating said element also passing through said contact means.
 6. The pulse generator as defined in claim 1, wherein said element comprises a bimetallic snap disc, said first circuit means including first contact means closed by said bimetallic snap disc when in said first position, said second circuit means including second contact means closed when said bimetallic snap disc is in said second position.
 7. A pulse generator as defined in claim 5, including circuit load means connected in series with said element when In said first position.
 8. The pulse generator as defined in claim 7, including resistor means connected in parallel with said circuit load means.
 9. The pulse generator as defined in claim 8, including manually operated switching means connected to said first circuit means and said second circuit means for switching the pulse output signal of said pulse generator, said regulating means comprising variable resistor means connected in circuit with said switching means.
 10. The pulse generator as defined in claim 1, including motor means; and control circuit means connected to said first circuit means and said second circuit means for controlling the operation of said motor in relation to the position of said element. 